Pico

I decided to drive the car to work today since it's a nice 60 degree sunny day out.
I noticed that the car warmed up fine (little below the half way point on the gauge)
but as I started driving to work the cars temperature slowly went down to the C.
It started raising again once I pulled into my parking spot at work..

I'm assuming it's most likely just in need of a Thermostat replacement right?
Did some research and I believe that to be the case, but want to cover everything
else it could possibly be?

Anyone on the board deal with the exact same issue?
Did you fix it by having the Thermostat replaced?

Bob1982

I would say your thermostat is stuck open.

acmoc

Check the thermostat, if the bottom hose stays hot while the top hose id cold, your thermostat is likely good and your problem is air pockets in your coolant.

Pico

Did a test yesterday when we replaced the axle, it's definitely the Thermostat. Got it on order already, as well as new front rotors, and new pads.
I ran into another little possible issue that the car seems to have, but I'll post that in another thread because it's completely different than the
thermostat issue.

B20VtecVillain

Certainly sounds like a thermostat issue to me. When you replace it, make sure to do a good bleed on the system to remove all the air, and check your cap to make sure it's in good order. B/D series engines are pretty sensitive to air in the cooling system so it's really critical to get it all out. Also, if your using factory a full factory cooling system I would strongly recommend using the Honda blue coolant. Standard "universal" green coolant will work, but it leaves the water jackets, hoses, radiator, water pump etc much dirtier from corrosion over time than the OEM blue coolant. I've seen cars with 200k+ miles and 20+ years on factory cooling systems that look amazingly clean inside and out due to being properly serviced with the right fluids. I've also seen rebuilds with only a few years/50k miles that look horrible. Best way to do it on a Honda, drain everything you can of the old coolant. Just pulling the radiator petcock will only drain about 2/3 of what's in the vehicle. If your not super mechanically savvy, just drain the rad, fill it back up with water. Run the car till operating temp, shut it down and drain the rad again. Repeat that process 2-4 times until what you drain is all clear. At this time it is also a good idea to remove the overflow tank, drain and clean it then reinstall. After this, do a final drain of the rad. Fill the radiator with Honda coolant;I have actually seen many people use an aftermarket reproduction available from auto part stores so They don't have to go to the dealership and it seems to work just as good . After you have the rad filled, leave the cap off and start the car. Turn the HVAC to full hot, heat on high. Let the car run for about 20 mins untill it is at full operating temp and the Tstat opens. When it does, the level of coolant in the radiator will drop, just keep adding little by little as needed to keep it full. Once the engine is fully hot, Tstat open and the coolant level no longer fluctuates you are done; put the cap on and turn off the car. A few helpful tips: ONLY use distilled water in your cooling system. Tap water or similar WILL cause corrosion inside the system. Distilled water is a $1 a gallon at the local Walmart and you only need a few gallons for the job even with flushing. Second, while the engine is hot and radiator is full and air free before you put the cap on, Rev the engine a bit and look for a rise in the coolant level, I.e. It's full to the brim at idle but when you rev it the level overflows and spills out. This is an early sign of a failing head gasket as it means cylinder pressure is getting into the coolant passages. Doing the brief process I listed above will give you a perfectly functioning cooling system that will stay that way for a long time. With OEM coolant and a clean system to start, coolant changes can be back burnered and handled once every 40k miles or so. Good luck.

bheinen74

running "straight water" in a Honda is not how I would flush. Doesn't the coolant have lubricant in it for the water pump?

acmoc

Yes, coolant has lube in it to condition and extend the life of the seals and water pump.
Plus in cold climates you can crack your block with straight water
Buy full strength antifreeze and a gallon of distilled water and make your own 60/40 mix
Way cheaper than buying premix 50/50